In recent years, the digital camera function comes standard with the personal device typically represented by the mobile phone. Further, there has been an increasing demand based on the social demand for a small-sized monitoring camera. This has created a heavy demand for further reduction in the size and weight of a camera module. In the meantime, the camera module used in the personal device or small-sized monitoring camera is required to meet the demands for more and more sophisticated functions such as an auto-focusing function and image stabilization function.
An actuator for driving the optical system and mechanical system is essential to ensure sophisticated functions of the camera module. This requires an actuator capable of providing sophisticated functions while meeting the demand for more compact and lightweight configuration.
In this situation, an actuator using a shape memory alloy attracts attention as an actuator providing sophisticated functions while meeting the demand for more compact and lightweight configuration. The shape memory alloy is typically represented by a titanium-nickel alloy, and can be defined as the alloy that, after having been subjected to deformation below a predetermined temperature, comes back to the original status due to martensite transformation by raising the temperature above that temperature level. This property of the alloy is utilized to provide the performance of the actuator by heating.
In the shape memory alloy having such excellent properties, the driving principle is based on temperature. Thus, the characteristics of the shape memory alloy tend to depend on the ambient temperature, and it needs to be controlled by detecting the ambient temperature, when it is put into practical use.
One of the techniques proposed so far in the field of the catheter wherein the shape memory alloy is used as an actuator, for example, is a method of detecting the ambient temperature using a temperature sensor such as a thermistor installed in addition to the shape memory alloy (Unexamined Japanese Patent Application Publication No. H06-114003).
However, the technique proposed in the Unexamined Japanese Patent Application Publication No. H06-114003 uses a temperature sensor such as a thermistor installed in addition to the shape memory alloy. This arrangement requires a space for the temperature sensor, and is not suited to meet the requirements for downsizing. This technique also requires an additionally installed temperature detecting circuit for detecting the temperature using the temperature sensor, which means that the technique requires an increased space and much more number of parts, with the result that a substantial cost increase will occur. Further, due to the geometric and spatial restrictions, it may not possible to place the temperature sensor close to the shape memory alloy, and this may result in poor precision of detection of the temperature.